Phase modulating system



May 14, J. sAwA 2,001,107

PHASE MODULA TING SYSTEM Filed July 31, 1934 FIG.

INVEN TOR J. 05A WA A r romysr Q ing the operation of the system of Fig.1.

Patented May 14, 1935 a i I w 2,001,107

UNITED STATES PATENT OFFICE 'Juichi Osavva, Mita, Shibaku, Tokyo, Japan,assignorto Western Electric Company, Incorporated, New York; N. Y., acorporation of New York 7 Application July 31, 1934, Serial No. 737,696I H In Japan August 24, 1933 I 6 Claims. (Cl. 179-171) This inventionrelates to modulating systems with sections 6 and 1 andmidpoint 8. Afeedandparticularly to those in'which the phase of back transformer 9has one winding connected 2. carrier wave is varied in accordance withto the grid of tube I and the other connected signals. I I between theplate and cathode of tube I through 5 The general object of theinvention isto transaseries tuning condenser I0. A signal source II 5latea signal wave into a succession of phase is connected to the grid oftube I by means of variations in a carrier wave. an input transformerI2. The grid circuit of A specific object isto diminish amplitudevaamplifier 3 is connected between the grid of tube riations of thecarrier Wave in the process of I and the transformer midpoint 8. Theoutput 10' phase modulation. r circuit of amplifier 3 is coupled to theantenna 10 Existing systems of "phase modulation which system 4 in anentirely conventional manner. insure a close correspondence betweenphase va- In the operation of the system of Fig. l, the

-riation and signal amplitude show very little carrier generator 2develops a carrier voltage amplitude variation provided the phase changeacross the secondary windingsfi and 'I,the value is relatively small. Ifthis range be exceeded, the of which voltage in each winding is denotedby 5 accompanying amplitude modulation may be E/2. In the absence offeedback, the entire great. voltage E is impressed between the grid andIn accordance with H the invention, a carrier cathode of tube I. Withthe feedback circuit wave of substantially fixed amplitude andvaconnected, as shown, a carrier current, denoted riable phase isgenerated by means of a vacuum by IP, in the plate circuit develops afeedback 20 tube having a reactive feedback connection be-' voltage,denoted by EM, acrosstransformer 9. tween its plate and grid circuits.The voltage The carrier voltage between grid and cathode, fed back tothegrid circuit is in fixed quadrature designated Ec, is modified by thefeedback, but relation with the grid voltage. The resultant is alwaysdetermined by the equation. p

vectorial value of the sum of the grid voltage and v 25 the feedbackvoltage is always substantially equal E= E -l- E (1) r to the impressedcarrier. voltage, which latter T may be supplied from'a constant voltagesource. in which each voltage is required to be expressed The grid andfeedback voltages may be varied as a vector quantity.

by means of a-source of signal waves but the The plate circuit of tube Imay be tuned to 30 quadrature relation of the voltages will hold thecarrier frequency by means of the condenser throughout the variation.Furthermore, the load Ill. At resonance the onlymaterial impedance.impedance offered by the vacuum tube'to the of the plate circuit is theinternal plate-to-cathcarrier source is not materially affected by theode resistance which is herein designated R0 introduction and operationof the signal source. andhas a conductance value equal to the re- 35 Thelocus of the grid potential is given in'the ciprocal of R0 which will becalled S. The carvector representation by a circular arc. The rarierplate current I]? is then given by the equadius vector, whichcorresponds to the voltage betion tween the grid and the midpoint of thecarrier E source, has the properties here desired. Ac- I K (2) 40cordingly, the output wave is taken from across 1 s p thus insuring aphase modulated where ,LL is the amplification factor of the tube. Wfree from amplitude modulation- The voltage across either thetransformer 9 or The invention Will be morefully understoodthe condenserII! is in quadrature with the plate from the following detaileddescription in 6011 current and proportional thereto. In the system 45,

J c i with the drawing, of hi illustrated, the feedback voltage is takenfrom g- 1 shows a Preferred embodlment of h the transformer and isproportional to its mu- Ventwn? and tual impedance. The feedback voltageis then Fig. 2 is a vector diagram useful in explaindetermined by theequation In Fig. 1, a modulator tube I is shown con- E =jwMIp, (3)necting a carrier source 2 to an amplifier 3 and an antenna system 4.The carrier source is conwhere :i is the operator indicating quadrature,

nected to the grid of tube I by means of a transto is 21r times thecarrier frequency and M is the former 5 having a divided secondarywinding mutual inductance of the transformer 9. 55

Substantially Equation (2) in Equation (3) gives E =jwM E S,

which indicates that EM and EG are always in quadrature with each otheralthough their relative values may vary. Since the vector sum of EM andEG is always equal to the impressed voltage E, it is evident that thelocus of the grid potential must lie upon a circular arc in the vectorfield. This relation is shown in Fig. 2 wherein EG and EM are plotted atright angles and of such relative magnitudes as to sum up vectorially tothe value E. The phase angle between EG and E is denoted by b. Vfnilethis angle is variable by changing either E6 or EM, the latter byvarying S, the vector EG always terminates upon the semi-circular arehaving E as the di-. ameter.

Inspection of Fig. 2 reveals that the radius vector lies between themidpoint of the diameter and the junction of Ed and EM. This vector hasa constant length /2E and a variable phase angle 5. The vectorcorresponds to the voltage generated in the system of Fig. 1 betweenpoint 8 and the grid of tube l. The voltage between these points isdenoted E and is impressed between the grid and cathode of amplifier 3.In this way a voltage of constant amplitude and variable phase isimpressed on the amplifier 3 and delivered in amplified form to theantenna system 4 The phase is varied by means of the signal source i Ishown connected to the grid circuit of tube I in a well known manner tovary the plate circuit conductance in accordance with a signal wave.

What is claimed is:

1. A phase modulating system comprising a vacuum tube with a cathode, ananode and a control grid, a divided carrier source with accessiblemidpoint, the outer terminals of said source being connectedrespectively to the grid and the cathode of the tube, means to feed backa carrier wave from the anode circuit to the grid circuit in quadraturewith the instantaneous carrier voltage between the grid and the cathode,a load circuit bridged between the midpoint of the carrier source andthe grid of the tube, and a signal source adapted to vary the anodecurrent of the tube, whereby the phase of the carrier voltage across theload circuit is varied at a signal rate while the amplitude of saidcarrier voltage is rendered substantially independent of the signal.

2. A phase modulating system comprising a vacuum tube with a cathode, ananode and a control grid, a divided carrier source with accessiblemidpoint, the outer terminals of said source being connectedrespectively to the grid and the cathode of the tube, an anode circuitincluding a branch series resonant to the carrier frequency, means totransfer into the grid cir cuit a voltage developed across one elementor" said series resonant branch, a load circuit connected between thegrid of the tube and the midpoint of the carrier source, and a signalsource adapted to vary the anode current of the tube, whereby the phaseof the carrier voltage across the load is varied while the amplitude ofsaid carrier voltage remains unchanged.

3. A phase modulating system comprising a vacuum tube with a cathode, ananode and a control grid, a divided carrier source with an accessiblemidpoint, the outer terminals of said source being connectedrespectively to the grid and the cathode of the tube, an inductance anda capacitance connected in series between the anode and the cathode ofthe tube, said inductance and capacitance being resonant to the carrierfrequency, inductive coupling means to couple said inductance with thegrid of said tube, a signal source adapted to vary the anode current ofthe tube, and a load circuit connected between the grid of the tube andthe midpoint of the carrier source, whereby phase modulation of thecarrier source is effected substantially without amplitude modulation.

4. A phase modulating system comprising two vacuum tubes, each having acathode, an anode and a control grid, a divided carrier source with anaccessible midpoint, the outer terminals of said source being connectedrespectively to the grid and the cathode of the first tube, means tofeed back a carrier wave from the anode of the first tube to its grid inquadrature with the instantaneous carrier voltage between said grid andcathode, a signal source adapted to vary'the anode current of the firsttube, said second tube having its grid and cathode terminals connectedrespectively to the grid of the first tube and-the midpoint of thecarrier source, whereby the anode current of the second tube isphase-modulated without material amplitude modulating effect.

5. A phase modulating system comprising a vacuum tube with a cathode, ananode and a control grid, a transformer with a divided secondarywinding, a carrier source connected to the primary winding of the inputtransformer, the extremities of the secondary winding being connectedrespectively to the grid and the oathode of the tube, means to feed backa carrier wave from the anode to the grid in quadrature with theinstantaneous carrier voltage between the grid and the cathode, a loadcircuit connected between the grid of the tube'and the midpoint of thesecondary winding of the transformer, and a signal source adapted tovary the anode current of the tube, whereby the phase of the carriercurrent in the load is' varied at a signal rate while the amplitude ofthe carrier current is substantially constant.

6. A phase modulating system comprising a vacuum tube with a cathode, ananode and a control grid, a divided carrier source with an accessiblemidpoint, the outer terminals or" said source being connectedrespectively to the grid and the cathode of the tube, meansto feedback acarrierwave from the anode to the gridin quadrature with'the carriervoltage existing between the grid and the cathode, a load circuitbridged between the midpoint of the carrier source and the grid of thetube, and a signal source adapted to change the internal anodecathoderesistance of the tube, whereby phase modulation free from objectionableamplitude modulation is effected.

JUICHI OSAWA.

